The present invention relates to a pressure accumulator as well as to a method of producing the same.
More particularly, it relates to a pressure accumulator which has a housing with at least one pressure medium opening, a substantially cylindrical diaphragm chamber arranged inside of the housing and having a side wall which is at least partially deformable, and a pressure medium chamber arranged outside of the diaphragm chamber.
The present invention also relates to a method for producing a pressure accumulator with a housing having at least one pressure medium opening, a substantially cylindrical diaphragm chamber arranged inside the housing and having a side wall, at least one substantially cylindrical diaphragm chamber which is arranged inside the housing and has a side wall which is at least partially deformable, and a pressure medium chamber arranged outside the diaphragm chamber.
Such pressure accumulators are used in particular in motor vehicle braking devices. A hydraulic pump is associated preferably at the outer side with the pressure medium chamber under pressure, so that potential energy is available for a braking device which is coupled with wheel. An elastic force is available due to a compressible diaphragm chamber. This elastic force is counteracted by the force which is applied by the pressure of the pressure medium, so that the pressure accumulator function is produced. The diaphragm chamber is filled with gas. An elastic force is therefore made available due to the at least partially deformable side wall and due to the compression of the gasses located in the diaphragm chamber.
In the case of uptightness of such a diaphragm chamber gas exits the inner space of the diaphragm chamber into the pressure medium chamber and thereby under unfavorable conditions gas can penetrate into the braking device. This can lead to a damage and operational error of the braking system.
Accordingly it is an object of the present invention to provide a pressure accumulator, and a method for producing the same which avoid the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a pressure accumulator, in which the pressure medium chamber is limited at least partially by a partially permeable material which allows exit of gas from the pressure medium chamber and prevents exit of pressure medium from the pressure medium chamber.
In this way it is possible that gas which is in the pressure medium chamber is removed purposefully from the pressure medium chamber. Thereby it is prevented that gas enters the braking device and can lead to operational disturbances. The pressure accumulator, despite leaking diaphragm, remains operational.
Preferably, the side wall of the diaphragm chamber is bellows-shaped. Due to the bellows-shaped design, the diaphragm chamber is deformable so that elastic force required for the pressure accumulator operation is available.
It is also advantageous when a first head side of the diaphragm chamber is sealingly closed with a metal bottom. In this way, a solid limit of the diaphragm chamber is available, which imparts a shape stability to the side wall.
Preferably the second head side of the diaphragm chamber is sealingly closed with a filling member. Through this filling member, gas such as for example air can be filled in the diaphragm chamber, so that due to the compressibility of the gas, a counterpressure to the pressure of the pressure medium is applied. Preferably, the pressure medium opening is closeable by a metal bottom. When the pressure inside the diaphragm chamber exceeds the pressure of the pressure medium, then the pressure medium chamber is closed against the other components of the braking device, so that the hydraulic pressure assumes a lower value than the gas pressure in the diaphragm chamber.
It is advantageous when the pressure medium chamber is limited at a side by a partially permeable material, which in mounted condition of the pressure accumulator is the upper side. Finally, the gas which flows from the diaphragm chamber by a leakage in the diaphragm in the pressure medium chamber is driven by the action of the gravity force in the region of the partially permeable material. Therefore the gas can exit through the partially permeable material into the atmosphere.
It is advantageous when the pressure medium chamber is arranged ring-shaped around the diaphragm chamber, and when the partially permeable material is formed as a ring-shaped element which limits in ring-shaped manner the pressure medium chamber. The ring shape of the partially permeable material is especially favorable to limit the cylindrical pressure medium chamber which expands around the diaphragm chamber to the upper side of the pressure accumulator.
It is especially useful when the partially permeable material is a ceramic material. A ceramic material can have a porosity provided by steam treatment or a special compaction, which allows a gas exchange but prevents a liquid exchange. Also, ceramic diaphragms are produced with a smaller pore size, which allow a gas exchange and prevent a liquid exchange. It is especially advantageous when the side of the partially permeable material which faces the pressure medium chamber is provided with a pore size of less than 10 A. Thereby it is prevented that the liquid infiltrates through capillary forces into the ceramic material.
Preferably, the side of the partially permeable material which faces away the pressure medium chamber is provided with a sealing pack which acts as a valve. The sealing pack allows the exit of gas from the pressure medium chamber into the atmosphere. It however prevents the entry of gas from the atmosphere into the pressure medium chamber. The later is especially advantageous in connection with the evacuation of the pressure medium chamber.
The present invention deals with a method, in accordance with which at least one opening of the housing is closed with a partially permeable material. In this way it is possible to remove from the pressure medium chamber gas which enters the pressure medium chamber. Thereby it is prevented that the gas enters the braking device and leads to operational disturbances. The pressure accumulator, despite leaking diaphragm remains operational.
It is especially advantageous when a head side of the diaphragm chamber is closed, in that, the side wall of the diaphragm chamber is mounted on a filling member by a laser welding process. Also different welding processes are suitable for producing the connection between the diaphragm chamber and the filling member, while a laser welding process provides for especially good results.
Furthermore, it is advantageous when the partially permeable material is formed as a ring-shaped element, and the ring-shaped element is pressed in a region between the housing and the filling member. This pressing of the ring-shaped element closes the housing in a fluid-tight manner, while a gas exchange remains possible because of the partial permeability.
An especially useful connection in view of the pressure tightness of the element is provided between the ring-shaped element and the filling member when a caulking connection is produced. Thereby a pressure accumulator can be produced which can withstand high pressures in the region of approximately 200 bar.
The present invention is based on a surprising consideration that it is possible to provide a pressure accumulator which despite a leaking diaphragm maintains its operational ability, wherein it prevents that gas due to a leak in a diaphragm reaches the braking system. This is achieved with the use of a partially permeable material which is arranged at a suitable point of the pressure accumulator and thereby relieves gas into atmosphere. As for the fluid, the material is however not permeable, so that the principal operation with respect to the pressure medium remains not negatively changed.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.